In a liquid crystal display device, a thin-film EL (electroluminescence) display device, an organic EL display device or the like, an amorphous silicon (a-Si) film has been conventionally mainly used as a semiconductor film that functions as a channel layer of a TFT (thin-film transistor) which is a semiconductor device.
In recent years, attention has been focused on a composite oxide including indium (In), gallium (Ga) and zinc (Zn), i.e., an In—Ga—Zn-based composite oxide (also referred to as “IGZO”), as an alternative material to a-Si. A higher carrier mobility can be expected in an IGZO-based oxide semiconductor as compared with a-Si.
For example, Japanese Patent Laying-Open No. 2008-199005 (PTD 1) discloses that an oxide semiconductor film mainly composed of IGZO is formed by a sputtering method by using an oxide sintered body as a target.
Japanese Patent Laying-Open No. 2008-192721 (PTD 2) discloses an oxide sintered body including indium and tungsten (W), as a material suitably used when forming an oxide semiconductor film by the sputtering method and the like.
In addition, as a material suitably used when forming an oxide transparent electroconductive film by a vacuum vapor deposition method such as an electron beam vapor deposition method, an ion plating method and a high-density plasma-assisted vapor deposition method, Japanese Patent Laying-Open No. 2006-347807 (PTD 3) discloses an oxide sintered body including indium oxide having W solid-dissolved therein, including W with a ratio of atomic number of W to In being equal to or higher than 0.001 and equal to or lower than 0.034, and having a density (apparent density) of equal to or higher than 4.0 g/cm3 and equal to or lower than 6.5 g/cm3.